The first police-baton blow to he head easily doubles the suspect over.

But the blows keep coming — two, three, four — sending him crashing to the lobby floor, where he curls up and writhes as the baton rises and falls again and again, striking his head, his neck, his shoulders.

On Day Two of testimony in a chilling police-brutality trial, Manhattan prosecutors today released the first images from a video that caught the 2008 police beating of a suspect in a West 93rd Street housing project.

Housing cop David London — a 15-year NYPD veteran and married father of three kids — had been on routine patrol when he noticed the front door of the Hostas Houses complex had been propped open and left his squad car to shut it.

That’s when he ran into Walter Harvin — a young Army vet who had recently returned from the battlefields of Iraq.

Harvin, wearing a white doo-rag and t-shirt, is seen on the tape rushing to enter the building, where his mother lives, before London shuts the door.

That’s where the two begin an encounter that would end with Harvin drenched in blood and bruises from more than 20 baton blows and kicks to his upper body — the final few of which rained down on him even after London and his partner had managed to handcuff the injured man.

“Everybody in America should see that video,” said Harvin’s mother, Cora Page, 46, during a break in court.

“But I don’t want to see it,” she added.

And she didn’t, remaining in a courthouse hallway as it was screened again and again for jurors.

“People need to see it so they can see how cops treat people,” added Harvin’s uncle, Earl Jones, 55.

The multiple cameras in the housing project hallway clearly capture the lead-up to the beat-down. Harvin pushes past the cop to enter the lobby, and the two exchange words in apparent anger, though the video has no audio.

At one point, as London prevents Harvin from going into the lobby elevator, Harvin shoves the cop’s chest with both hands.

The two are then seen staring eye-to-eye as London raises his baton for the first time. The first blow, to the left side of Harvin’s head, causes Harvin to crumple in two. But the blows continue, and even as they do, Harvin still screams and taunts, the partner told jurors.

“I came from Iraq!” the partner remembered Harvin shouting.

“I was in the Air Force, too!” the cop answers, still swinging.

Defense lawyers say the missing audio — the taunts, the threats and the fact that Harvin keeps thrashing, even in cuffs and even in the police car as he bleeds from his injuries en route to the precinct — show that London’s force was necessary.

Prosecutors counter that nothing justifies 20 blows to a man who, at least mid-way through, has clearly become incapacitated.

Traumatized by the incident, Harvin has disappeared, his family said. He is not expected to testify.